The interaction of macrophages with an obligate intracellular microbe (Toxoplasma gondii) and other facultative or obligate intracellular microbes will be studied. The intracellular events associated with phagocytosis of these microbes by macrophages from normal and immunized animals will be studied using phase contrast and electron microscopy, radioactive labelling techniques to follow metabolic changes in cell function and determination of generation times under various cell conditions, including: immune cells, elicited cells, cells which are activated or those stimulated in vitro. The events to be followed will include observation of phagocytic rates, changes in membrane organization such as appearance of complement receptors, response to cyclic nucleotides and glucosamine uptake, need for protein synthesis in microbe inhibition, secretion of substances by the cell and the morphologic changes in cell organelles during infection. The effect of sensitized lymphocytes and lymphokines on the intracellular events in macrophages after phagocytosis of toxoplasmas will continue to be investigated. Further characterization of the toxoplasma antigen induced lymphokine will be done. It is expected that study of this lymphocyte macrophage model will add important dimension to our knowledge of intracellular parasitism and cellular immune responses.